Paris — If you are a Russian oligarch, a dictator, or you're trying to make a nuclear bomb, it’s probably good to have Maya Lester on your speed dial.

The British lawyer is a leading counsel for those who find themselves on international blacklists. As the crisis in Ukraine and ensuing struggle between Russia and the West takes uncertain turns, demand for such specialists is rising – not least because it's far easier, with the help of lawyers like Ms. Lester, to get off of an EU sanctions list than an American one.

But her job might also be set to get more challenging – something that many in Washington would welcome.

To stem the growing number of blacklist targets challenging their cases in European courts, the EU is debating whether to amend its procedures to be more in line with those of the US. Currently, the government must share its evidence with the defendant, potentially allowing them to see classified information. The proposed rules would allow judges to consider as evidence any information that could harm EU member states, while still withholding it from defendants.

“It’s hugely controversial,” says Ms. Lester, particularly among groups who say the opaqueness of the US system tramples human rights. But others say the procedure could help Europe more effectively use sanctions as a foreign policy tool. As it works now, European authorities are often weighed down by fears of litigation.

“Whenever we have to do a listing, one of the concerns is, how are we going to survive in court? There is this selection bias in the beginning,” says Francesco Giumelli, an assistant professor of international relations at the University of Groningen in the Netherlands and author of “The Success of Sanctions.”

The case against sanctions

As Ukraine has marched steadily toward civil war after Russia annexed Crimea in February – a crisis that only showed signs of possible abatement yesterday, after Russian President Vladimir Putin called to postpone an independence referendum planned in eastern Ukraine – the US and Europe have imposed sanctions on Russian officials. But the EU has not targeted Mr. Putin’s inner circle to the degree that the US has, instead focusing almost exclusively on individuals tied to the annexation itself or to fomenting violence in eastern Ukraine.

Europe has billions at stake if relations deteriorate with Russia. It must find consensus with 28 members before issuing any sanction. But the threat of legal proceedings plays a significant role too in its reticence.

“If the EU would put somebody on the list who is just close to Putin, in court they’d have to prove how this person is linked to what is happening in Crimea, which is not very easy,” says Paul Ivan, an expert on European sanctions at the European Policy Centre in Brussels. With each successful challenge, he says, the entire system is weakened. “One of the dangers is that it undermines the credibility of the sanctions regime.”

Sanctions against individuals expanded in the late 1990s, on a growing belief that comprehensive sanctions that hurt general populations, as in Iraq, were ineffectual at best, a humanitarian tragedy at worst. But individuals began challenging cases in court, a task that got much easier in Europe in 2008, after a landmark case that Lester worked on.

Yassin Abdullah Kadi, a Saudi businessman with alleged ties to Al Qaeda was sanctioned by the United Nations Security Council at US request after 9/11. But in the EU, where the sanctions were applied, Kadi's legal team – which included Lester – argued that the listing violated his rights since he was not shown the evidence against him. They successfully got him removed from the EU list; he is still on the US one.

The case set a strong precedent that individuals must be notified – and shown evidence – of why they are listed so that they may fairly challenge the listing and defend their rights. The case also set a precedent for using European law to overturn a UN decision.

The US has shown frustration with the European system since then, underlined in a Wikileaks cable from Brussels in 2009. “Legal challenges continue to threaten the EU’s use of targeted economic sanctions as an instrument of international security and foreign policy,” it reads. “US economic sanctions are rarely effective unilaterally, and we cannot risk losing the use of one of our few non-military coercive tools because EU courts believe they are somehow illegitimate.”

In Europe, all individuals in the court system, no matter their nationality, are guaranteed due process. If it's found they were denied it, it’s grounds for striking someone off the list. In the US, authorities have far more flexibility to use classified intelligence without sharing it with often foreign challengers. It's become a highly legalized process in Europe, whereas in the US, it is more political, says Mr. Ivan.

“The US gives them the right to challenge the listing, but the system is much tougher to challenge and actually win,” he says. “In the EU, the court has taken a very active role."

A new legal regime?

Caseloads have soared in recent years with the number of sanctions placed on Iranian individuals accused of working on nuclear proliferation. Lester counts between 100 and 200 such cases that have been heard in the European court system – enough to fill four thick binders in her office in downtown London. She herself has litigated some 30 cases, involving hundreds of clients, which have sent her to Luxembourg’s European Court of Justice on a monthly basis. She estimates that she's gotten about half of her clients removed from blacklists.

Still, she says, victory is elusive, since clients are often simply relisted. And it might become even more elusive. That’s in part because, as exemplified in the case of Russia, Europeans today are becoming more selective about whom they target.

A new proposal under consideration in Europe could further “take the wind out of the sails” of the litigation, says Gavin Sullivan, a UK solicitor who has represented a number of individuals targeted by the UN Al Qaeda sanctions regime. The European Council is studying a proposal that would let judges view evidence in extremely sensitive security cases without allowing the client or their lawyers to see it. While proponents of the new rules see an opening for a more effective system, human rights defenders condemn them as creating “secret hearings” that would take them down the US route.

“It’s a decision which changes the architecture of the European judicial system in a very significant way with very little public discussion,” says Mr. Sullivan.

It’s an ongoing ethical debate, similar to those over waterboarding and the use of drones, says Mr. Giumelli. “For civil liberties advocates, [they focus on] respecting the rights rather than the outcome. Officials would rather say we need to get the bad guys, even if on the way we violate some rights,” he says.

Lester, who runs a blog called European Sanctions, says she worries about the direction in which Europe could head. She says she realizes that some of her clients “are not popular causes,” and she says her friends tease her when it’s time to board a flight to Tehran to represent the “bad guys.” But she says she is simply trying to protect individual human rights against the state.

“This is not a campaign by me to get the sanctions system to unfold," she says. "It will work better if … people have trust that it’s not someKafkaesque nightmare of blacklists but a well thought through, fair process.”